Various platemaking processes for lithographic printing plates as well as plate materials have been proposed, as seen in the wide use of computers. From the standpoint of practical use, a lithographic printing original plate is prepared by transferring block copies from a positive/negative film. On the other hand, electrophotography and Silver lithographic plates, which are directly made from block copies without using a positive/negative film, have also been developed. Further, so-called "Computer to Plate (CTP)" type plate material has been proposed. In the use of this plate material, graphic information made by computer type setting and DTP (Desktop Publishment) is directly printed onto a plate by using a laser or a thermal printing-head without visualized hard media. This plate material has not been applied to practical use yet. However, since CTP enables the rationalization and shortening of the platemaking process as well as the reduction of material costs, there is a great demand for practical use of the CTP in a field such as news printing where CTS (Cold Type System) is employed for all printings.
Photosensitive plates, thermosensitive plates, and plates made by electrical energy have been known as CTP type plate material. The photosensitive plate and the plate made by electrical energy have not been used in practice, since not only the price of those plates are higher than that of conventional presensitized plates (PS plates) but also platemaking machine used for preparing them are large-sized and expensive. Moreover, they have a problem in that they require waste treatment of a developing solution.
The thermosensitive plate materials are developed for use in light printing, e.g., for printing in offices. Japanese Patent Application Laid-Open Nos. 64747/1988 and 113290/1989 disclose printing plate materials whose thermosensitive layer arranged on a substrate contains a heat-fusible resin and a thermoplastic resin, and which are changed from hydrophilic to oleophilic by fusing with thermal imaging. U.S. Pat. Nos. 4,034,183 and 4,063,949 disclose printing plate materials prepared by irradiating a hydrophilic polymer layer coated on a substrate with laser to change hydrophilic to oleophilic. However, these printing plate materials have disadvantages in that the non-image areas are stained with ink due to a heat-fusible resin presented on the surface of the layer, in that the printing durability of the plates is insufficient, and the ability to design various types of desired plates is limited. Japanese Patent Application Laid-Open Nos. 108588/1991 and 8575/1993 disclose a printing plate material prepared by coating a substrate with a thermal recording layer composed of a microcapsuled heat-fusible substance and a binder resin, and heating it to change to oleophilic. However, they do not show sufficient printing durability since the microcapsuled heat-fusible substances used for those plates are not reactive. On the other hand, Japanese Patent Application Laid-Open Nos. 164596/1987 and 164049/1987 disclose a lithographic printing original plate having a recording layer which comprises a hydrophilic binder polymer containing an active hydrogen and a block isocyanate, and platemaking processes using the same. These plate materials further need a developing process in order to eliminate non-printed areas after being imaged.
Furthermore, the direct type of lithographic printing plate materials include a direct writing type lithographic printing plate material whose image areas are formed on the surface of the hydrophilic layer by external methods such as ink-jet and toner transfer. Japanese Patent Application Laid-Open No. 1587/1987 discloses a printing plate material coated with a non-reactive microcapsuled heat-fusible substance, which becomes a toner receiving layer by thermal imaging. The printing plate material cannot be used as a printing plate until the toner receiving layer accepts oleophilic toner. That is, the printing plate material does not obtain image areas after being imaged.
Thus conventional thermosensitive printing plate materials are poor in printing durability or in oleophilic property so that they are used only for light printing. In addition, some of the thermosensitive printing plate materials require a developing process during platemaking.
As described above, conventional techniques are insufficient in the performance of the printing plates and platemaking machines, in the efficiency of platemaking process as well as in the price of printing materials, printing plates and platemaking machines for practical use. The present invention aims at solving the above-mentioned problems of the conventional direct type lithographic printing plate materials for offset printing. One object of the present invention is to provide a low-price lithographic printing original plate which does not collect scum, in which a lithographic printing plate showing high printing durability and high accuracy in size and prints having clear images are obtained. The other object is to provide a lithographic printing original plate which is prepared without a developing process requiring waste treatment of developing solution and which can be made without use of specific large-scaled and expensive platemaking machines, and a platemaking process using the same.